document `conf` a bit
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+# Jekyll Configuration
+
+This folder contains different configuration files for the Jekyll build which is triggered via `gulp build` and similar commands (`gulp serve` etc.).
+
+Files present after checkout:
+
+- `_config.yml` is the main Jekyll config file
+- `_version.yml` defines the latest version of the docs
+- `_dev.yml` is used for normal builds
+- `_prod.yml` is used when the `--prod` option is used for the build
+- `_nodocs.yml` is used when the `--nodocs` option is used for the build
+
+Some files are generated by the build process itself:
+
+- `_defaults.yml` defines different config values for different parts of the docs
+
+To learn more about how to control the build with these files, have a look at: https://jekyllrb.com/docs/configuration/
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